MEXICO CITY, Dec 13 (Reuters) - Mexico's antitrust

watchdog Cofece ruled that Walmex, the local unit of

U.S.-based Walmart ( WMT ), engaged in a monopolistic practice

related to its suppliers, the retailer said in a statement on

Friday.

Walmex said it has been ordered to pay a fine of 93,366,000

pesos, or about $4.6 million, and that it will challenge the

watchdog's ruling.

The Cofece resolution follows an investigation that lasted

just over four years.

($1 = 20.2422 Mexican pesos)